Azeotropic distillation of hydrocarbons with sulfur dioxide



Jan. 3, 1950-l H v HEss AzEoTRoPIc DIsTLLTIoN' oF HYDRocARoNs wma SULFUR DIoxIDE Filed March 23, 1948. 2 Sh`eetS'-,Sheet 1 PAPA FF/N/C A250 TPOPE @LEF/Mc Fs/nus) s Se lk S 3:

IN VEN TOR.

Ho ARD V s ORNEY Patented Jan. 3, 1950 AZEOTROPIC DISTILLATIN F HYbRO- CARBON S WITH SULFUR DIOXIDE Hawai-a v. Hess, Fishkill, N. Y., assigner to 'rile Texas Company, New York, N. Y., a corporation of Delaware Application March 23, 1948, Serial No. 16,506

3 Claims. (Cl. 2oz-42) 'I'his invention relates to certain improvements in the azeotropic distillation of hydrocarbons with sulfur dioxide to effect a separation into oleflnic and parafflnic fractions.

The use of sulfur dioxide as an azetrope former has been proposed but has been diilcult in practice because of the formation of polysulfones. These polysulfones are solid or plastic resinous materials and the formation of them by the contacting of the sulfur dioxide with olefins results in a reduction in the yield of desired products. Furthermore it frequently happens that the formation of the resinous material is of such extent as to cause a plugging of the lines in the distilling equipment and render the operation inoperative.

I have discovered that the formation of these resinous materials may be completely eliminated by avoiding the contacting of the sulfur dioxide and they hydrocarbon mixture containing olens while at temperatures at which the reactions producing the polysulfones occur and by conducting the azeotropic distillation at temperatures above that of the formation of polysulfones. 'I'he temperature necessary to prevent the polysulfone formation will vary with the particular olens contained in the hydrocarbon'mixture which is to be separated into oleflnic and paraffinic fractions. The maximum temperatures at which polysulfone formation occurs with certain olens has been found to be approximately as follows:

Isobutylene 39-41 Butylene-2 (cis and trans mixture) 109-111 Butylene-l 145-150 Propylene 188-192 In accordance with my invention the formation of polysulfones is avoided by preheating prior to contacting so that when the hydrocarbon and sulfurV dioxide are brought into contact for azeotropic distillation the composite temperature will be above the temperature of polysulfone formation. It is to be observed that this temperature above the maximum for formation of polysuliones should be maintained generally throughout the distilling zone or at least in all portions of the equipment at which material proportions of olens and sulfur dioxide may be in contact.

In practicing the invention the sulfur dioxide and the hydrocarbon mixture to be treated are separately heated to a temperature above the maximum temperature of polysulfone formation prior to being brought into contact with each other. 'I'hus in a continuous operation the sulfur dioxide and hydrocarbon mixture are passed thru 2 separate heating zones and brought to the desired temperature andare then discharged into the distilling tower wherein the azeotropic distillation takes place. The two preheated streams may be commingled to enter the tower as a single stream or they may be admitted to the tower as separate streams. An advantageous operation is to admit the sulfur dioxide stream at a point above that of the entry of the hydrocarbon stream. Due to the selective solvent action of the sulfur dioxide for olens this latter method promotes a selective extraction to take place which thus aids in effecting the separation between the parafiins and olefins.

In the drawings:

Fig. 1 is a flow diagram illustrating one method of practicing the invention.

Fig. 2 is a graph showing the temperature gradient through the distilling tower in a typical operation.

Fig. 3 is a graph showing the percentage of unsaturates in various portions of the tower in a typical operation.

Referring to Fig. 1 the element I0 represents Aa distilling tower adapted for the azeotropic distillation. The tower is provided with suitable bubble trays, packing or contact material adapted for efficient vapor-liquid contacting. A heating coil II 'is provided at the bottom and a cooling coil I2 is disposed at the top.

The sulfur dioxide is passed through a heating coil I3 wherein it is heated to a temperature somewhat exceeding the maximum or ceiling temperature of polysulfone formation. The hydrocarbon charge, such as Ca, C4 and Cs hydrocarbons containing mixtures of olens and parailns, is passed through a heating coil I4 wherein it is similarly heated to a temperature above this ceiling teinperature. The eliluent from the heating coils I3 and I4 passes to a manifold I5 by which the sulfur dioxide and hydrocarbon may be discharged into the tower at various intermediate points therein. As will be readily seen the eiluent from the two streams may be merged in the manifold for entry into the tower as a single composite stream or the sulfur dioxide and hydrocarbon may be admitted separately with the sulfur dioxide entering at a point above that of the hydrocarbon.

In the tower I0 azetropic distillation takes place with the paraffin azeotrope passing overhead as vapor and the olefin or olefin and sulfur dioxide collecting in the bottom of the tower. The vapors pass through a condenser I6 and the condensate is collected in a receiving drum II. The olefin fraction is withdrawn from the bottom of the tower.throughl aline il'. The temperature inthe reboiler section ofthe tower is maintained kby the heating coil I tat a temperature vsomewhat exceeding the temperature of the eilluent 'from the heating coils so as to assure that throughout the tower and at least where any material proportions of olefins are present the temperature will be maintained above the ceiling temperature of polysulfone formation of the olens present. The tower is held under a superatmospheric pressure adapted to raise the boiling points -of the components so that the temperature may be held above the temperature of polysulfone formation and the parafiin azeotropes distilled overheadl In one method of operation only sufficient sulfur dioxide is charged to form azeotropes with the parafins in the hydrocarbon mixture and in this method the parailin azeotropes are distilled overhead and the olefin lfraction which will be substantially free from S02 is withdrawn as the bottom fraction. It may be mentioned that when operating in this way the composition of the bottoms may not always immediately reach a condition where it is entirely free from SO2. A certain reservoir of liquid is necessarily maintained in the reboiler section of the tower and consequently an interval must elapse in order for the bottoms to attain the desired degree of olefin purity.

In another method of operation anexcess of sulfur dioxide over that required to form azeotropes with 'the paraiiins is charged to the system and in such case sulfur dioxide will be present in the olefin residue withdrawn from `the tower.

In an example of the invention a hydrocarbon stock consisting of approximately equal portions of normal butane and butylenes-Z was heated to a temperature of 140 F. and continuously introduced to the tower at a point about W7 up from the bottom of the tower. Sulfur dioxide in a .proportion in excess `of that requiredV to form azeotropes with the butane was preheated to the same temperature and continuously introduced at a point about $6 up from the bottom of ,the tower. The tower was held under a gauge pressure of 180 lbs. per sq. in. The lreboiler temperature was 175 F. and the overhead temperature 140 F. The following table shows the number of hours on stream with the weight per cent of saturates in the overhead, the Weight per cent of unsaturates in the bottoms and the reflux ratio in the several periods: r

Overhead Bottoms Wt Hours on Rel-lux Wt. Per Cent Per Cent Stream Saturetes Unsaturates Ratio In another example of the invention the hydrocarbon stock containing equal portions of normal butane and butylenes-2 and the sulfur dioxide in amount only sufficient to -form azeo-A the bottoms and the reflux ratio duringv the several periods'.

Overhead Bottoms Htufrn Wt. Percent Wt. Per cent lgig Betumtes Unsaturates Fig. 3 'shows the percentage of unsaturates in 0 samplesjof the liquid withdrawn from various points in the tower and in the bottoms and overhead distillate during a period in this run.

With the stock treated in each of these runs the top temperature at which polysulfone formation could have taken place would have been about 109111 F. By maintaining minimum temperatures in the one case of 140 F. and in the other of F. the operation was conducted safely above the level of polysulfone formation and an effective separation into parain and olen fractions was accomplished.

The method in which only sufficient sulfur dioxide is used to form azeotropes with the parafn has the advantage that the olenic residue free from sulfur dioxide may be readily withdrawn without any precautions as regards the formation of polysulfones. When operating with an excess of sulfur dioxide over that required for the formation of parafllnic azeotrope with the result that SO2 is present in the olefinic residue the Withdrawal line should be kept at a temperature above the maximum temperature of polysulfone formation. In reference to the presence of oleiins in the parafnic overhead, it has been determined that as regards a mixture of butane and butylenes-Z for instance, proportions of olefin up to as much as 5% gave no evidence of polysulfone formation even at low temperatures. In viewof the fact that in the practice of the invention an overhead product containing even less than 5% olefins may be obtained, it will be lseen that there is ordinarily no diiliculty in cooling and condensing the overhead product. However, instead of passing the overhead parailinlc azeotrope through a condenser coil as indicated in Fig. 1, the vapors may be passed directly to a tower and washed with water or caustic solution When operating with sulfur dioxide present inv 'the residue withdrawn from the azeotropic distilling tower quantities of monosulfone may be present in which case the olenic residue may be passed through a heat treating zone by which the monosulfone is readily converted into olen and SO2-and the products then washed with water or caustic solution to recover the olen product.

Although a preferred .embodiment of the invention has been described herein, it will be understood that various changes and modincations may be made therein, while securing to a greater or less extent some or all of the beneiits of the invention, without departing from the spirit and scope thereof. A f

I claim:

1. In the azeotropic distillation of hydrocarbon stocks consisting of parains and monoolefns with sulfur dioxide as the azeotrope former, the process that comprises separately heating the hydrocarbon and the sulfur dioxide prior to contacting, then contacting the heated hydrocarbon and sulfur dioxide at a temperature above the temperature of polysulfone formation and conducting the azeotropic distillation at temperatures in excess of such temperature.

2. In the azeotropic distillation of hydrocarbon stocks consisting of parafns and monoolens with sulfur dioxidel as the azeotrope former, the process that comprises separately heating the hydrocarbon and the sulfur dioxide prior to contacting to a temperature above the temperature adapted to sustain polysulfone formation, then contacting the heated hydrocarbon and sulfur dioxide and effecting azeotropic distillation at a temperature above that of polysulfone formation.

3. In the azeotropic distillation, with sulfur dioxide as the azeotrope former, of hydrocarbon stocks comprising essentially paraflins and monoolens and substantially free from diolefins, the process that comprises separately heating the hydrocarbon and the sulfur dioxide. then contacting the heated hydrocarbon and sulfur di- REFERENCES CITED The following references are of `record in the le of this paltent:

i UNITED STATES PATENTS Number Name Date 2,186,524 Frey Jan. 9, 1940 2,207,608 Britton et al July 9, 1940 2,316,860 Guinot Apr. 20, 1943 2,332,493 Petry et al Oct. 19, 1943 2,333,856 Gerhold Nov. 9, 1943 2,356,840 Frey Aug. 29, 1944 2,382,473 Frey Aug. 14, 1945 2,390,934 Gregg Dec, 11, 1945 2,412,880 Frey Deo. 17, 1946 

1. IN THE AZEOTROPIC DISTILLATION OF HYDROCARBON STOCKS CONSISTING OF PARAFFINS AND MONOOLEFINS WITH SULFUR DIOXIDE AS THE AZEOTROPE FORMER, THE PROCESS THAT COMPRISES SEPARATELY HEATING THE HYDROCARBON AND THE SULFUR DIOXIDE PRIOR TO CONTACTING, THEN CONTACTING THE HEATED HYDROCARBON AND SULFUR DIOXIDE AT A TEMPERATURE ABOVE THE TEMPERATURE OF POLYSULFONE FORMATION AND 